1. Field of the Invention
This invention relates to locks and particularly to magnetic locks. Most particularly, this invention relates to a magnetic lock which is highly pick resistant.
2. The Prior Art
Magnetic locks have been known for many years. Thus, for example, U.S. Pat. No. 2,931,953 granted to W. Barney on Apr. 5, 1960 discloses a latching device wherein a movable member is locked against movement by a transversely extending magnetic pin which is normally biased into a complementary aperture in a stationary part as by gravity. However, when a key is inserted into the lock, the key carries a magnet that is poled so as to repel the magnetic pin in the movable member whereby to unlock the lock. The problem with a device such as Barney's is that so long as a minimum field strength is provided for the magnet in the key, it will suffice to repel the movable magnetic pin whereby to unlock the Barney lock. This being the case, it is a relatively simple matter to unlock Barney by having two keys with the magnets therein of considerable magnetic strength and being oppositely poled. By a simple trial and error process requiring a maximum of two trials, the Barney lock could be unlocked. A similar problem is encountered with Felson U.S. Pat. No. 3,111,834 wherein a plurality of magnetic pin tumblers are provided in the plug of the lock, each being biased to bridge the shear plane of the lock by a like poled magnet in the shell. When a key is inserted which bears magnets that are like poled to the pin tumblers, the tumblers will be repelled by the magnets in the key whereby to clear the shear plane and unlock the lock. Again, there is no consideration for the amount of field strength required for the magnets in the key of the Felson lock, so long as a minimum field strength is attained. Thus, for each pin tumbler in the Felson lock, there are only two possibilities. This being the case, the number of keys necessary to cover all possibilities is only 2.sup.n, where "n " is the number of magnetic tumblers in the Felson lock. For example, a five-pin tumbler will require only a set of 32 keys, a practical number for a burglar to carry to open the lock.
A similar problem exists in the magnetic lock described in Felson U.S. Pat. No. 3,416,336 which is similar to the earlier discussed Felson patent save for the fact that the pin tumblers are moved by magnetic attraction rather than by magnetic repulsion. The same inherent weaknesses may be found in this patent as in the earlier Felson patent. This is likewise true of the locks described in Wake U.S. Pat. No. 3,518,855.
Other prior art patents known to applicant to disclose magnetic locks are Hallmann U.S. Pat. No. 3,566,637, Hallmann U.S. Pat. No. 3,681,727, Hallmann U.S. Pat. No. 3,782,147 and Pelto U.S. Pat. No. 3,837,195. However, none of the structures described in these patents appears to be as pertinent as the references discussed in detail hereinbefore.
In U.S. Pat. Application Ser. No. 539,285 filed by the applicant herein on Jan. 8, 1975, and in the continuation-in-part thereof, Ser. No. 637961, filed concurrently herewith, the contents of both of which are hereby incorporated by reference in their entireties, a magnetic lock is described and claimed which requires a key having magnets disposed therein for repelling magnetic pin tumblers, which key magnets must not only be poled properly, as was true in the prior art patents discussed above, but which magnets must also be of particular and different field strengths, whereby to render the lock highly pick resistant. However, the structure described in these applications calls for the rotor and stator of the lock to define two radially spaced apart shear planes and for the pin tumbler magnets to be repelled to a location between the two shear planes for unlocking the lock. As will be understood hereinafter, the present application discloses a lock having the advantages of the prior application lock, but requiring only a single shear plane.